Ureteral stents are fundamental to the practice of Urology. These devices allow one to bypass and drain an obstructed ureter, determine urine output from a particular renal unit, and inject contrast to study the upper urinary tract. With the advent of newer methods to manage upper urinary tract stones, such as extracorporeal shock wave lithotropsy (ESWL) disclosed in U.S. Pat. No. 4,913,683 issued to Gregory, and urethroscopy, the use of ureteral stents will continue to grow.
The ideal ureteral stent should allow one to measure urine output from a particular renal unit, drain even tenaciously purulent material, allow injection of contrast for imaging and finally remain indwelling and self contained if longterm ureteral stenting or drainage is required.
The presently available devices consist of external or internal ureteral stents. Both types are usually passed through the ureteral meatus via a cystoscope, though they can be placed openly through different sites in the urinary tract.
Externalized ureteral stents drain the upper urinary tract and pass through the bladder, exiting the urethra and draining into an external collecting device. They allow drainage through ports and a central lumen or channel, and can be irrigated as needed to drain tenacious and obstructing material. By draining externally, the output from the involved renal unit can be carefully monitored. Contrast can be injected as needed to evaluate the upper tract.
Unfortunately, these devices are not self contained and must be secured or they will migrate and be extruded by ureteral peristalsis. They therefore are not suitable for longterm outpatient care.
With this objective in mind, internalized ureteral stents were developed. The most commonly used type is a plastic stent with a curl at both the proximal and distal ends, i.e., a "double-J" stent. The curls are straightened over a central stiffening wire in order to pass the stent, but are reformed when the stiffening wire is removed. The proximal curl prevents distal migration and thereby keeps the device in the renal pelvis. The distal curl is positioned in the bladder to allow completely internalized drainage. No urethral catheter is needed to secure this type of stent, making it ideal for outpatient management.
U.S. Pat. Nos. 4,957,479 issued to Roemet; 4,931,037 to Wetterman; 4,913,683 to Gregory; 4,820,262 and 4,307,723 to Finney 4,790,810 to Pugh, Jr. et al.; 4,790,809 to Kuntz; 4,787,884 to Goldberg; 4,713,049 to Carter; 4,671,795 to Mulchin; and U.S. Pat. No. 4,610,657 to Densaw all show this general approach, while U.S. Pat. Nos. 4,813,925 to Anderson, Jr. et al., and 4,531,933 to Norton et al. show a variation of this concept by using helixes to replace hooks.
The devices shown by these patents, however, have disadvantages. The urine output from the involved renal unit cannot be recorded as only total urethral urine output can be recorded and this would include both kidneys. Also, since the distal end of the stent is internalized, it is not possible to irrigate the tube should it become obstructed. Under these circumstances the obstructed stent could be more detrimental than beneficial as it would occlude an already narrow ureteral lumen. Since the ureteral stent can become obstructed without any external indication, the situation can become dramatically acute before it is realized that the internalized stent is no longer serving its purpose. Lastly, as the stent is not externalized, contrast cannot be injected if needed to image the upper tract.
U.S. Pat. No. 4,913,683 to Gregory allows injection of contrast via a small lumen in the stiffening wire. This lumen, however, is too small to allow reliable and accurate monitoring of urine output or drainage and irrigation of tenacious debris from the involved kidney.